The present disclosure relates to disk brake caliper pistons and piston systems, such as are used for various vehicles including automobiles, trucks, aircraft and the like. Embodiments of the disclosure include pistons having provision for a screw actuated braking capability including those having a threaded actuator system for a parking brake and a pressure actuated capability for additional braking capability such as braking capability actuated by a fluid pressure source such as a pneumatic or hydraulic pressure source. In various embodiments, the screw actuated braking capability can be actuated by a motor such as an electric motor or any other suitable type of motor or by actuation of a lever.
Brake pistons and disk brake pistons, such as disclosed herein, can be of any suitable construction, such as being made from steel, forged steel, plastic, ceramic and other metals which can be machined or otherwise manufactured to provide external sealing surfaces and an internal cavity. As shown in FIG. 1, an embodiment of a piston 1 has an internal cavity 2 with a threaded spindle 3 engaging an internally threaded nut 4 which upon relative rotation between the spindle 3 and the nut 4 the nut moves linearly toward or away from the brake pad end of the piston 5. Upon relative rotation in a first direction, the nut 4 moves toward the brake pad end of the piston 5 and then engages and pushes against the brake pad end of the piston, with the brake pad end of the piston 5 engaging the brake pad 6 directly or indirectly and causing a braking action between the brake pads 6, 7 and the rotor. In some embodiments, the movement of the nut 4 toward the brake pad end of the piston 5 can be done in conjunction with a pressure force being applied to the piston, and the force applied by the nut 4 to the brake pad end of the piston 5 can supplement the pressure force or can serve to partially or fully maintain the force applied to the piston by the pressure system when the pressure is reduced or eliminated. In some embodiments, the spindle 3 and nut 4 can be part of a parking brake, such as an electromechanically actuated parking brake actuated by a motor 8.
Upon relative rotation in a second direction, the nut 4 moves away from the brake pad end of the piston 5 and reduces and/or removes the force of the nut 4 acting upon the brake pad end of the piston 5.
Fluid pressure actuation of a brake system as shown in FIG. 1 causes piston 1 to move against brake pad 6, which in turn moves against a brake rotor (not shown.) The incomplete return of the brake pad, after moving against the brake rotor, causes drag and a braking effect results. Movement of the brake piston 1 during braking can be caused by the presence of pressure against one side of piston 1. However, return movement of piston 1 when the fluid pressure is released is also desirable, for example to allow a vehicle to roll freely without brake drag slowing the vehicle and leading to unnecessary fuel consumption and wear of parts. However the release of the fluid pressure will generally not provide a positive retraction of the brake piston 1 and cessation of the braking effect. In some embodiments, a square cut o-ring 22 can provide a small amount of positive retraction of the piston 1 when the fluid pressure is relieved. In some embodiments, this square o-ring 22 can also provide sealing of the braking fluid within the system of the brakes. In some embodiments, the retraction provided by the square o-ring can occur because upon application of fluid pressure, the movement of the piston causes a distortion of the square o-ring due to friction between the square o-ring 22 and the piston 1. Upon release of the fluid pressure, square o-ring 22 is allowed to move back to its undistorted position, and by way of friction between the square o-ring and the piston, drags the piston 1 back to its previous position. However, under some conditions, such as hard braking, or where brake parts are old or worn, the friction between the square o-ring 22 and the piston 1 can be reduced or the amount of movement is greater than the distortion of the square o-ring 22 can accommodate. As a result, the piston 1 can in some cases slip along the square o-ring 22 and at least a portion of the return effect can be lost. In addition, the design of the o-ring for brake return can in some instances compromise the design of the o-ring for sealing, and vice versa. Accordingly, alternate designs of brake piston retraction which provide a more positive return of the brake piston and which separate the functions of fluid sealing and piston return are desirable.